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The provision of artificial nests can improve the conservation status of threatened bird species that are limited by nest-site availability. The shortage of natural cavity nesting sites is one factor limiting the population growth of the Southern Ground Hornbill Bucorvus leadbeateri. In an 1,800 km2 study area in north-eastern South Africa, 31 wooden nest-boxes were installed during 2002–2015. We investigated the relationships between nests, as well as environmental and social factors, with breeding. Generalised linear mixed models were fitted to the observational data and identified positive relationships between breeding attempts and each of home range size and the previous year’s rainfall; as well as positive relationships between breeding success (amongst the groups that attempt breeding) and each of earlier breeding, nest height and thickness of the nest cavity wall. The provision of nest-boxes increased the number of breeding groups and although breeding success also increased initially, it later declined as the density of breeding groups increased above 20 groups. Although nest-boxes alone did not increase overall breeding success, they are an effective conservation tool to enhance the population of Southern Ground Hornbills if spaced optimally, to enhance reproductive output in areas where suitable nest-sites are scarce or lacking.

Summary

Introduction

Competition over resources, both between individuals of the same species and between different species, plays a crucial role in natural selection (Danchin et al., 2008). Competition is believed to play a major role in regulating the local coexistence of individuals and species (Gause, 1934); therefore, adaptations should have evolved to reduce intra- as well as interspecific resource competition (review in Gause 1934; Brown and Wilson 1956; Hardin 1960; Amarasekare, 2003; Chase and Leibold, 2003). In principle, competition can be avoided through resource partitioning (arthropods: Behmer and Joern, 2008; invertebrates: Pianka, 1973; birds: Garcia and Arroyo, 2005; mammals: Azevedo et al., 2006; Sushma and Singh, 2006). Partitioning of food resources (of focus in this chapter) can be expressed in different ways. First, a food resource might be used by several individuals and/or species in different proportions. For instance, even though three sympatric primate species in Bolivia (Callimico goeldii, Saguinus labiatus and S. fuscicollis) show dietary overlaps, the relative proportion of shared food resources in their total diet differ between species (Porter, 2001). Second, food resources might be temporally partitioned: shared resources may be used at different times of the day and/or during different seasons. This is illustrated by the diurnal versus the nocturnal feeding patterns of different lemur species in Madagascar (Petter, 1962), as well as the varying levels of nocturnal activity between two sympatric species of foxes in Brazil (Vieira and Port, 2007). Third, food resources might be spatially partitioned. The same resources can then be used by competitors who occupy different areas or microhabitats. Spatial separation of resources can occur on a local scale as well as on a larger geographic scale. One example is given by two mouse lemur species, Microcebus murinus and M. berthae, in western Madagascar. These solitary foragers show a high degree of dietary overlap, but their coexistence appears to be facilitated by spatial separation on a local scale (Dammhahn and Kappeler, 2008a, 2008b). On an intraspecific level, spatial separation is most prominent in territorial species where individuals exclude each other from access to the resources within their territories, and reduce direct competitive interactions by marking them with olfactory cues (Paquet, 1991; Fawcett et al., 2012), acoustic signals (Chivers and MacKinnon, 1977; Robinson, 1981) or visual displays (Peek, 1972).